1. Field of the Invention
The present invention relates to a fluid device, such as a fluid pump or a hydraulic motor, having a plurality of expanding and contracting working chambers defined by interacting teeth of a gerotor gear set. Specifically, the present invention relates to a commutation apparatus for directing fluid flow to and from such working chambers.
2. BACKGROUND ART
Hydraulic devices, such as pumps or motors, which have a plurality of expandable and contractable working chambers formed by interacting teeth of a gerotor gear set are known. Typically, the gerotor gear set includes a stator having internal teeth and a rotor having external teeth. The rotor, which has one less tooth than the stator, is eccentrically disposed within the stator. The rotor is mounted for rotational and orbital movement relative to the stator and is supported by and guided in such movement by the teeth of the stator. The interacting teeth of the rotor and stator define the plurality of working chambers which expand and contract during the rotor's movement.
Various valve constructions have been developed for directing fluid into and out of the expanding and contracting working chambers. Such valve constructions are known in the art as commutator valves. Examples of such commutator valves are disclosed in U.S. Pat. Nos. 4,087,215, 4,219,313, and 4,411,606. The commutator valves disclosed in these patents include mechanically rotatable valve members. The valve members have precisely located openings and lands which, during rotation of the valve members, are timed (i) to selectively block fluid flow to or from working chambers, (ii) permit fluid flow to expanding working chambers, and (iii) permit fluid flow from the contracting working chambers.
The commutator valve arrangements of known hydraulic devices often require precise machining and/or assembly. In a hydraulic motor, such commutator valves do not permit precise control of the speed of an output shaft of the hydraulic motor nor precise control of the final rotational position of the output shaft when the motor is stopped. Such precise control is necessary for the application of a gerotor type hydraulic motor in robotics and automated manufacturing. Such an application would require a motor to have a high load carrying capacity, a relatively high operating speed, precise position control of the output shaft when the motor is stopped, an ability to provide incremental movement of the output shaft, and reversible operation.